Loghain doesn't recognize who helps him at first. Just hears a woman's shout, sees a dress, but even at his worst he wouldn't have abandoned her to the fate of the demon's attention. If nothing else, if she escapes too that would put them at odds, and the best way to make sure this demon doesn't surprise him again is to see it dead.

An opening is all he needed, and it's what he gets. One deep breath, two - it's broken off the chase of him to go after the new victim that just hurt it. Loghain sees the knife in the back (THAT looks familiar, but he can't place it in the narrowed focus of the fight) and rushes it, his own at the ready so he literally jumps upon her back, yanking out the smaller knife from the demon's back and using both to reach in front and stab her in the chest before cutting her throat so deep it's halfway to decapitation. Even then when it falls he falls upon it, stabbing it someplace that looks vital every time it so much as twitches until it goes still, white dress now a deep red.

Loghain brings a hand up to wipe some of the blood spray off of his face. Then looks up.

Oh. Now there's recognition of who saved him.

"... your highness," he says, wiping the smaller knife of Rowan's off on the leg of his breeches and holding it out to her, hilt first.